System and method for controlling a vehicle

ABSTRACT

A vehicle is provided including an electronic power steering system, an electronic throttle control system, and a stability control system.

RELATED APPLICATIONS

This application is a divisional of Non-Provisional patent applicationSer. No. 14/928,121 filed Oct. 30, 2015, which claims priority toProvisional Patent Application Ser. No. 62/073,724 filed Oct. 31, 2014;the subject matter of which are incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to a vehicle and more particularly tocontrol strategies for recreational and utility vehicles.

BACKGROUND AND SUMMARY

Some recreational vehicles, such as all-terrain vehicles (ATV's),utility vehicles, motorcycles, etc., include a power steering system.Electronic power steering systems often use a detected ground speed todetermine the level of steering torque assist to provide to the steeringassembly. In these systems, the power steering will not functionproperly when ground speed data is faulty or unavailable. In addition,the calibration of a power steering unit may drift over time, resultingin a steering offset bias.

The stability of recreational vehicles may be assessed by stabilitytests, such as a static (KST) stability test, a rollover resistancerating (RRR) test, and a J-Turn test. Many recreational vehicles lack anactive stability control system.

In an exemplary embodiment of the present disclosure, a vehicle isprovided including an electronic power steering system, an electronicthrottle control system, and a stability control system.

More particularly in a first embodiment, a power steering method for avehicle is disclosed, where the method includes detecting, by acontroller of a power steering system, a speed of an engine of thevehicle; determining, by the controller, a power steering assist levelbased on the engine speed; and outputting, by the power steering system,steering torque assistance to a steering assembly of the vehicle basedon the power steering assist level.

In another embodiment, a power steering method for a vehicle includesdetecting, by a controller of a power steering system, an error with aground speed feedback signal; changing, by the controller, a powersteering assist control mode from a first control mode to a secondcontrol mode in response to detecting the error with the ground speedfeedback signal, wherein in the first control mode the controllerdetermines a power steering assist level based on the ground speedfeedback signal and in the second control mode the controller determinesthe power steering assist level based on at least one of a throttlevalve opening, a detected engine speed, and a predetermined fixed groundspeed; and outputting, by the power steering system, steering torqueassistance to a steering assembly of the vehicle based on the powersteering assist level.

In another embodiment, a power steering method for a vehicle includesdetecting, by a controller of a power steering system, a selected gearof a transmission of the vehicle; determining, by the controller, apower steering assist level based on the selected gear of thetransmission and a user torque input to a steering assembly of thevehicle; and outputting, by the power steering system, steering torqueassistance to the steering assembly of the vehicle based on the powersteering assist level.

In another embodiment, a power steering system for a vehicle, includes asteering assembly including a steering shaft; a sensor operative todetect a speed of an engine of the vehicle; and a power steering unitincluding a controller in communication with a motor, the motor beingoperably coupled to the steering shaft, the controller including controllogic operative to determine a power steering assist level based on theengine speed, the controller controlling the motor to output steeringtorque assistance to the steering shaft based on the power steeringassist level.

In another embodiment, a method for controlling a power steering systemof a vehicle including: detecting, by a controller of the power steeringsystem, a trigger event; in response to detecting the trigger event,determining, by the controller, a torque offset of the power steeringsystem; and in response to the torque offset exceeding a threshold foreach of a plurality of occurrences of the trigger event, determining, bythe controller, a torque offset correction value; and controlling, bythe controller, a steering torque assistance applied by the powersteering system to a steering assembly of the vehicle based on thetorque offset correction value.

In yet another embodiment, a recreational vehicle includes a chassis; anengine supported by the chassis; a ground engaging member; a steeringassembly operably coupled to the ground engaging member; a powersteering system including a steering shaft, a power steering unit, and acontroller in communication with the power steering unit; and a torquesensor in communication with the controller, the controller beingoperative to detect a trigger event, in response to the detection of thetrigger event, determine a torque offset of the power steering systembased on output from the torque sensor, in response to the torque offsetof the steering shaft exceeding a threshold for each of a plurality ofoccurrences of the trigger event, determine a torque offset correctionvalue, and control a steering torque assistance applied by the powersteering system to the steering assembly based on the torque offsetcorrection value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary vehicle incorporating thecontrol strategies of the present disclosure;

FIG. 2 is a representative view of an exemplary control system of thevehicle of FIG. 1 including a vehicle and engine controller, atransmission controller, and a power steering unit;

FIG. 3 illustrates an electrical power steering unit incorporated into asteering assembly of the vehicle of FIG. 1;

FIG. 4 is a representative view of the power steering unit of FIG. 2;

FIG. 5 is a block diagram illustrating an exemplary method forcalculating a level of power steering assist according to someembodiments;

FIG. 6 is an exemplary graph illustrating power steering assist levelsbased on input steering torque and vehicle speed for low-range andhigh-range transmission gears;

FIG. 7 is a block diagram illustrating an exemplary method fordetermining whether a calibration of the power steering unit of FIG. 2is within a tolerance range;

FIG. 8 is a block diagram illustrating an exemplary method forcorrecting a calibration offset determined in the method of FIG. 7 thatis outside the tolerance range;

FIG. 9 is a block diagram illustrating an exemplary method for throttleoverride;

FIG. 10 is representative view of a stability control system of thevehicle of FIG. 1; and

FIG. 11 is a block diagram illustrating an exemplary method foradjusting active vehicle systems based on a terrain traversed by thevehicle of FIG. 1.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplification set out hereinillustrates embodiments of the invention, and such exemplifications arenot to be construed as limiting the scope of the invention in anymanner.

DETAILED DESCRIPTION OF THE DRAWINGS

The embodiments disclosed herein are not intended to be exhaustive orlimit the disclosure to the precise forms disclosed in the followingdetailed description. Rather, the embodiments are chosen and describedso that others skilled in the art may utilize their teachings.

The term “logic” or “control logic” as used herein may include softwareand/or firmware executing on one or more programmable processors,application-specific integrated circuits (ASICs), field-programmablegate arrays (FPGAs), digital signal processors (DSPs), hardwired logic,or combinations thereof. Therefore, in accordance with the embodiments,various logic may be implemented in any appropriate fashion and wouldremain in accordance with the embodiments herein disclosed.

Referring initially to FIG. 1, an exemplary vehicle 10 is illustratedthat implements the control strategies disclosed herein. Vehicle 10 isillustratively a side-by-side ATV 10 including a front end 12, a rearend 14, and a frame or chassis 15 that is supported above the groundsurface by a pair of front tires 22 a and wheels 24 a and a pair of reartires 22 b and wheels 24 b. Vehicle 10 includes a pair of laterallyspaced-apart bucket seats 18 a, 18 b, although a bench style seat or anyother style of seating structure may be used. Seats 18 a, 18 b arepositioned within a cab 17 of vehicle 10. A protective cage 16 extendsover cab 17 to reduce the likelihood of injury to passengers of vehicle10 from passing branches or tree limbs and to act as a support in theevent of a vehicle rollover. Cab 17 also includes front dashboard 31,adjustable steering wheel 28, and shift lever 29. Front dashboard 31 mayinclude a tachometer, speedometer, a display, or any other suitableinstrument.

Front end 12 of vehicle 10 includes a hood 32 and a front suspensionassembly 26. Front suspension assembly 26 pivotally couples front wheels24 a to vehicle 10. Rear end 14 of vehicle 10 includes an engine cover19 which extends over an engine 130 and transmission assembly 122 (seeFIG. 2). Rear end 14 further includes a rear suspension assembly (notshown) pivotally coupling rear wheels 24 b to vehicle 10. Other suitablevehicles may be provided, such as a snowmobile, a straddle-seat vehicle,a utility vehicle, a motorcycle, and other recreational andnon-recreational vehicles.

Referring to FIG. 2, an exemplary control system 100 of vehicle 10 isillustrated. Control system 100 includes a controller 102, such as avehicle control module and/or an engine control module, having vehiclecontrol logic 104 that controls the engine 130, various subsystems, andelectrical components of vehicle 10. Controller 102 includes one or moreprocessors that execute software and/or firmware code stored in aninternal or external memory 106 of controller 102. The software/firmwarecode contains instructions that, when executed by the one or moreprocessors of controller 102, causes controller 102 to perform thefunctions described herein. Controller 102 may alternatively include oneor more application-specific integrated circuits (ASICs),field-programmable gate arrays (FPGAs), digital signal processors(DSPs), hardwired logic, or combinations thereof. Controller 102 mayinclude one or more physical control modules.

Memory 106 is any suitable computer readable medium that is accessibleby the processor(s) of controller 102. Memory 106 may be a singlestorage device or multiple storage devices, may be located internally orexternally to controller 102, and may include both volatile andnon-volatile media. Exemplary memory 106 includes random-access memory(RAM), read-only memory (ROM), electrically erasable programmable ROM(EEPROM), flash memory, CD-ROM, Digital Versatile Disk (DVD) or otheroptical disk storage, a magnetic storage device, or any other suitablemedium which is configured to store data and which is accessible bycontroller 102.

Control system 100 further includes at least one vehicle battery 109(e.g., 12 VDC) for providing power to the electrical components ofcontrol system 100, such as controller 102, sensors, switches, lighting,ignition, accessory outlets, and other powered components. One or morespeed sensors 110 provide speed feedback to controller 102, such as theengine speed, vehicle speed, PTO shaft speed, or other drive linespeeds. For example, sensors 110 may include an engine RPM sensor, awheel speed sensor, a transmission speed sensor, and/or other suitablespeed sensors. A brake operator sensor 136 detects a position of a brakeoperator 134 and/or an applied pressure to brake operator 134 of vehicle10. Brake operator 134 may include a pedal, a hand brake, or anothersuitable operator input device that, when actuated by an operator, isconfigured to provide an operator brake demand to controller 102.

Controller 102 is operative to output an electrical signal to a throttlevalve actuator 112 to control a position or opening of a throttle valve114 of engine 130. Controller 102 electronically controls the positionof throttle valve 114 of engine 130 based on the detected position of athrottle operator 126 to regulate air intake to and thus the speed ofengine 130. Throttle operator 126 may include an accelerator pedal, athumb actuated lever, a twist grip, or any other suitable operator inputdevice that, when actuated by an operator, is configured to provide anoperator throttle demand to controller 102. A throttle operator positionsensor 128 coupled to and in communication with controller 102 providessignal feedback to controller 102 indicative of the position of athrottle operator 126. A throttle valve position sensor 116 providesfeedback to controller 102 indicative of the actual position or degreeof opening of throttle valve 114. For additional disclosure ofelectronic throttle control provided with controller 102, see U.S.patent application Ser. No. 13/152,981, filed Jun. 3, 2011, entitledELECTRONIC THROTTLE CONTROL, the entire disclosure of which is expresslyincorporated by reference herein. In an alternative embodiment, vehicle10 is an electric vehicle or hybrid-electric vehicle and includes one ormore electric motors for powering the vehicle, and throttle operator 126provides a torque demand to controller 102 for controlling the electricmotor(s).

Control system 100 further includes a power steering assist unit (EPAS)252 in communication with controller 102. In the illustrated embodiment,power steering unit 252 includes an electronic power steering unit 252operative to provide steering assist to the steering assembly of vehicle10, as described herein.

Vehicle 10 further includes a transmission controller 120 incommunication with controller 102 that is operative to control atransmission 122 of vehicle 10. Transmission controller 120 includes oneor more processors that execute software and/or firmware code stored inan internal or external memory of transmission controller 120. Thesoftware/firmware code contains instructions that, when executed by theone or more processors of controller 120, causes controller 120 toperform transmission control functions.

In one embodiment, transmission 122 is an electronically controlledcontinuously variable transmission (CVT). In this embodiment,transmission 122 further includes a sub-transmission 124 coupled to anoutput of the CVT 122. In one embodiment, sub-transmission 124 is gearedto provide a high gear (high range), a neutral gear, a low gear (lowrange), a reverse gear, and a park configuration for vehicle 10 ofFIG. 1. Fewer or additional gears may be provided with sub-transmission124. See, for example, the exemplary continuously variable transmissionand sub-transmission disclosed in U.S. patent application Ser. No.13/652,253, filed Oct. 15, 2012, entitled PRIMARY CLUTCH ELECTRONIC CVT,the entire disclosure of which is expressly incorporated by referenceherein. Alternatively, transmission 122 may include any other suitabletransmission types, such as a discrete ratio transmission, automatic ormanual transmission, hydrostatic transmission, etc. One or more shifters123 operated by an operator are configured to select a transmission gearof transmission 122 and/or sub-transmission 124.

One or more suspension sensors 138 provide feedback to controller 102indicative of a suspension height or displacement (e.g., compression orextension) of the vehicle suspension system 139. For example, suspensionsensors 138 may include shock position sensors and/or spring positionsensors providing position feedback of the shock absorbers and springsor other suspension components of vehicle 10. In one embodiment,suspension sensors 138 are positioned internal to shocks of suspensionsystem 139 or mounted to control arms of system 139. In one embodiment,a display 132 is coupled to controller 102 for displaying vehicleoperation information to an operator. Exemplary information provided ondisplay 132 includes vehicle speed, engine speed, fuel level, clutchposition or gear ratio, selected transmission mode (e.g., auto, manual,hydrostatic), a selected terrain mode (e.g., pavement, ice/snow, gravel,rock, etc.), transmission gear, etc. In one embodiment, controller 102communicates with one or more sensors/devices of vehicle 10 and/or othervehicle controllers via controller area network (CAN) communication.

Referring to FIG. 3, an exemplary steering assembly 180 and exemplarypower steering assist unit 252 of vehicle 10 of FIG. 1 is illustrated.Steering assembly 180 includes a steering wheel 182 coupled to asteering column 194. Other suitable operator steering devices may beprovided. Steering column 194 is in turn coupled to power steering unit252 through a steering shaft 250 coupled to steering column 194 at afirst U-joint 254 and coupled to power steering unit 252 at a secondU-joint 256. Power steering unit 252 is coupled to a steering rack 258through a third U-joint 260 and a fourth U-joint 262 with a steeringshaft 264 disposed therebetween. In another embodiment, third u-joint260, fourth u-joint 262, and steering shaft 264 are omitted such thatpower steering unit 252 is coupled directly to steering rack 258.

Steering rack 258 is coupled to ground engaging members 22 a of a frontaxle 108 of vehicle 10 through steering rods 266A and 266B,respectively. The steering rods 266A, 266B are coupled to respectivesteering posts provided on a respective wheel carrier of wheels 24 a(FIG. 1). The movement of steering wheel 182 causes movement of thesteering rods 266A, 266B, and this movement of the steering rods 266A,266B is transferred to the respective wheel carrier to rotate about anaxis to turn ground engaging members 22 a. For additional detail of anexemplary steering assembly, see U.S. application Ser. No. 12/135,107,filed Jun. 6, 2008, entitled VEHICLE, the entire disclosure of which isexpressly incorporated by reference herein.

In the illustrated embodiment, power steering unit 252 is an electricpower steering unit that receives power from the electrical system ofvehicle 10. In one embodiment, power steering unit 252 is programmableto account for different vehicle conditions and/or operator preferences.Referring to FIG. 4, an exemplary embodiment of a power steering unit252 includes a controller 246 and a motor 249, illustratively a directcurrent (DC) motor 249. Controller 246 includes one or more processorsthat execute software and/or firmware code stored in an internal orexternal memory to perform the power steering operations describedherein. Controller 246 receives a user torque input 240 from the vehicleoperator (through shaft 250 of FIG. 3), a revolutions per minute (rpm)input 242 from the power source (engine 130 or electric motor), and avehicle speed input 244 from a speed sensor 110. Inputs 240, 242, and/or244 may include CAN bus signals or discrete signals, such as frequencyor pulse input signals or analog voltage signals. Controller 246provides a current signal to electric motor 249 based on inputs 240,242, 244. Shaft 264 is mechanically coupled to shaft 250 (FIG. 3)through power steering unit 252. Motor 249 is also coupled to steeringshaft 264 through a gear set and provides assistance to rotate steeringshaft 264 in addition to the force applied through shaft 250 by theoperator.

The user torque input 240 is generated by turning steering wheel 182 andis measured by a torque sensing device 248 which is illustrativelyhoused within power steering unit 252. Torque sensing device 248measures the angular displacement between two shafts connected by atorsional element (e.g., one of the shafts responsive to the movement ofsteering shaft 250 or being the steering shaft 250). The angulardisplacement is converted to a torque value. The torque value isreceived by controller 246 and is used by controller 246 to determine anamount of assist which power steering unit 252 should provide throughmotor 249 and the direction in which the assist needs to be supplied(left turn or right turn). The vehicle speed input 244 is also used tovary the amount of assist provided by power steering unit 252 dependingon the speed of vehicle 10.

In one embodiment, controller 246 receives additional inputs 280 (e.g.,maximum RPM, maximum ground speed, transmission gear, etc.) used forcalculating the level of the steering torque assist, as describedherein. In one embodiment, controller 246 is in communication withcontroller 102 of FIG. 2 (which is illustratively external to powersteering unit 252) to obtain speed profiles and additional inputs 280.For example, memory 106 of controller 102 may include one or moreelectronic power steering (EPS) speed profiles 140, 142 (see FIG. 2)which define the amount of current to motor 249 of power steering unit252 based on vehicle speed, user torque input, and other variables tovary the torque assistance level provided to steering shaft 264. In oneexample, the speed profile 140, 142 has distinct constant assist levelsbased on vehicle speed and user torque input 240. In another example,the assist levels of the speed profiles 140, 142 vary over a range ofvehicle speeds. In one embodiment, the RPM input 242 provides anindication of whether engine 130 is running or not running. Controller246 may enable or disable the steering torque assist based on whetherengine 130 is running.

In one embodiment, a first speed profile 140 of FIG. 2 provides that atspeeds below a threshold speed power steering unit 252 provides a firstamount of steering effort and assist to steering shaft 264 and at speedsabove the threshold speed power steering unit 252 provides a secondamount of steering effort and assist to steering shaft 264, the secondamount being lower than the first amount. In one example, the secondamount is no assist. In one embodiment, the amount of assist varies overa range of speeds (e.g., proportionally or otherwise) and is not limitedto two discrete speeds.

FIG. 5 is a flow diagram 300 illustrating an exemplary operationperformed by power steering controller 246 (or vehicle controller 102)for determining a level of steering torque assistance provided by powersteering unit 252 to shaft 264 when vehicle speed feedback 244 is faultyor unavailable due to, for example, sensor error or other fault.Reference is made to FIGS. 2-4 throughout the description of FIG. 5.

At block 302, controller 246 detects the vehicle ground speed based onfeedback 244 from vehicle speed sensor 110. At block 304, controller 246determines whether the ground speed feedback 244 has an error. Forexample, a ground speed error may include the detected ground speedhaving an erroneous value or a value that exceeds the capability of thevehicle, the detected ground speed changing at a rate that exceeds athreshold rate (for example, a threshold rate that corresponds to amaximum possible change in vehicle speed of vehicle 10), or controller246 failing to detect a ground speed. If controller 246 does not detecta ground speed signal error, controller 246 performs normal powersteering control at block 306 based on the detected ground speed, speedmaps, and/or other suitable inputs, as described above. If controller246 detects a ground speed signal error at block 304, controller 246proceeds to block 308 to implement an alternative power steering assistcontrol scheme to determine the applied amount of power steeringassistance using inputs other than detected ground speed. In theillustrated embodiment, controller 246 implements the alternative powersteering assist control scheme illustrated in blocks 310-318.

At block 310, controller 246 detects the engine speed (RPM) of engine130 based on sensor output. At block 312, controller 246 calculates anapproximate throttle valve 114 opening percentage based on the detectedengine speed and a maximum engine speed value stored in memory, based onthe following Equation (1):

Percentage Full Throttle=(Detected RPM)/(Max. RPM)   (1)

In one embodiment, controller 246 optionally calculates an approximateground speed of vehicle 10 at block 314 based on the detected enginespeed, the preset maximum engine speed value, and a preset maximumground speed value of vehicle 10, based on the following Equation (2):

Approx. Ground Speed=[(Detected RPM)/(Max. RPM)]×(Max. Ground Speed)  (2)

At block 316, controller 246 calculates the level of power steeringtorque assist to apply to shaft 264. In one embodiment, controller 246calculates the steering torque assist level based on the estimatedthrottle valve 114 opening percentage determined with Equation (1) andthe user torque input 240 detected with torque sensing device 248. Forexample, for a greater estimated throttle opening, the torque assistlevel may be reduced for a same user torque input 240, and for a lesserestimated throttle opening, the torque assist level may be increased forthe same user torque input 240. The torque assist level for a given usertorque input 240 may have several discrete levels based on multiplethrottle opening percentage thresholds or may be proportional to thethrottle opening percentage threshold. In one embodiment, utilizing anestimated throttle opening based on engine speed with Equation (1),rather than utilizing an unfiltered, actual throttle opening detectedwith throttle valve position sensor 116 (FIG. 2), provides for smootheradjustment to the steering assist level by controller 246 as a result ofthe engine speed changing less rapidly than corresponding changes in thethrottle opening. As such, in this embodiment, the torque assist levelis configured to change less rapidly or abruptly than if the torqueassist level was based on the unfiltered, actual throttle openingpercentage detected with position sensor 116.

Alternatively, controller 246 may calculate the power steering torqueassist level based on filtered throttle valve position data. In thisembodiment, a smoothing or averaging filter is applied to the throttlevalve position feedback output by throttle valve position sensor 116(FIG. 2) to reduce the likelihood that rapid or abrupt changes in thethrottle valve position result in rapid or abrupt changes to the levelof steering torque assist, thereby providing a smooth transition betweenlevels of steering torque assist as the throttle opening changes. Thefilter may include logic in controller 246 operative to smooth oraverage the output signal from position sensor 116.

In another embodiment, controller 246 calculates the steering torqueassist level based on the estimated ground speed determined withEquation (2) and the user torque input 240 detected with torque sensingdevice 248. In this embodiment, controller 246 may use the estimatedground speed to determine the steering torque assist level based on thespeed profiles, such as speed profiles 140, 142 described herein. Insome embodiments, a predetermined offset is subtracted from theestimated ground speed from Equation (2) to account for potential errorsor inaccuracies in the ground speed calculation, and the resultingadjusted estimated ground speed is used by controller 246 to determinethe steering torque assist level. In some embodiments, controller 246may use filtered actual throttle valve position data, as describedabove, instead of the estimated throttle opening percentage to estimatethe ground speed in block 314, i.e., the maximum ground speed multipliedby the filtered (e.g., averaged or smoothed) actual throttle openingpercentage.

At block 318, controller 246 outputs a current request to motor 249 tooutput steering torque to shaft 264 at the steering torque assist levelcalculated at block 316.

In one embodiment, controller 246 provides zero steering torque assistabove a certain threshold, such as above a particular throttle openingpercentage threshold or above an estimated ground speed threshold. Inone embodiment, controller 246 provides larger or full steering torqueassist below a particular throttle opening percentage threshold or belowan estimated ground speed threshold.

In one embodiment, the maximum engine speed value considered at blocks312 and 314 represents the theoretical maximum speed that engine 130 iscapable of achieving, and the maximum ground speed value considered atblock 314 represents the theoretical maximum ground speed that vehicle10 is capable of achieving. In one embodiment, the maximum engine speed,maximum ground speed, and other predefined calibration values of FIG. 5are stored in a calibration file stored in controller 246 or that iscommunicated by controller 102 to power steering controller 246. Thecalibration file may further include the speed profiles 140, 142.

In some embodiments, controller 246 uses additional calibration valuesor inputs to further refine the steering torque assist level calculatedat block 316. For example, in some embodiments controller 246 furtheruses a selected gear of the transmission 122, as described herein. Insome embodiments, controller 246 further uses an engagement speed of aclutch of a CVT transmission 122 (FIG. 2) to determine the steeringtorque assist. For example, a delay may occur from when the engine speedfirst increases from idle speed to when the CVT transmission 122 engagesthe CVT belt and causes the vehicle to move. In particular, the CVTsheaves engage the belt at a threshold engine speed (i.e., an engagementRPM) to transfer torque to the wheels. Torque is not applied to thewheels over the low engine speed range between engine idle speed and thethreshold engagement engine speed. An exemplary engine idle speed is1200 RPM, and an exemplary threshold engine speed is 3000 to 3500 RPM,although other suitable idle and engagement engine speeds may beprovided depending on vehicle configuration. In some embodiments,steering torque assist is delayed or reduced by controller 246 until thethreshold engine speed is reached and the transmission 122 engages thebelt to rotate the wheels and move the vehicle.

Controller 246 may use other suitable variables or constants todetermine the steering torque assist. For example, controller 246 mayadjust the steering assist based on the driveline condition of thevehicle, including the transmission gear, the number of wheels driven bythe engine, and the state of the differential(s) 145 (FIG. 2), i.e.,open, locked, or controlled slip state. For example, the vehicle mayinclude a first driveline configuration wherein the engine drives twowheels 24 b of the vehicle 10 (i.e., 2WD) and a second drivelineconfiguration where the engine drives all four wheels 24 a , 24 b(FIG. 1) of the vehicle 10 (4WD). In one embodiment, controller 246applies more steering torque assist in the 4WD configuration than in the2WD configuration for a given user torque input. In one embodiment,controller 246 applies more steering torque assist in the lockeddifferential configuration than in the open differential configurationfor a given user torque input.

In some embodiments, controller 246 further receives at block 316 ofFIG. 5 an input indicative of a gear selection of transmission 122 ofFIG. 2. The transmission gear may be detected via CAN bus, proximitysensor, mechanical switch, operator input device, or other suitabledetection mechanisms. In this embodiment, controller 246 adjusts thelevel of the power steering torque assist at block 316 of FIG. 5 basedon the selected transmission gear. The selected transmission gear may bethe gear ratio of a discrete gear ratio transmission, a gear ratio of aCVT transmission, and/or a gear ratio of a sub-transmission. Forexample, in one embodiment sub-transmission 124 includes a low-rangegear and a high-range gear. The low range gear provides increased powerand lower speed operation than the high range gear. For example, the lowrange gear may be used for towing, plowing, rock crawling, hauling, orother work operations, and the high range gear may be used for travelingat higher speeds or in non-loaded conditions. In the illustratedembodiment, controller 246 provides increased levels of steering torqueassist in the low-range gear and reduced levels of steering torqueassist in the high range gear of sub-transmission 124.

FIG. 6 illustrates a graphical representation 330 of an exemplary torqueassist level mapping for low- and high-range gears of sub-transmission124 for a given estimated ground speed (Equation (2) described above)and/or a given estimated throttle opening percentage (Equation (1)described above). The x-axis represents the level of user torque input240 (FIG. 4), and the y-axis represents the level of steering torqueassist output by power steering unit 252, each represented in units ofNewton meters (N-m). In the illustrated embodiment, more torque assistis provided in the low-range gear at the given ground speed than in thehigh-range gear at the given ground speed across the range of usertorque input. In one embodiment, a torque assist curve, such as thecurve of FIG. 6, is stored in memory of power steering unit 252 for eachof a plurality of ground speeds and/or throttle opening percentages. Thetorque assist curves may also be received from controller 102 in acalibration file.

In one embodiment, vehicle 10 further includes an adjustable stabilizerbar 144 coupled to the front steering assembly, as illustrated in FIG.2. Stabilizer bar 144 includes an actuator controlled by controller 102(or controller 246 of FIG. 4) for variable adjustment. In oneembodiment, the engagement/disengagement and the stiffness of thestabilizer bar 144 is controlled and adjusted by controller 102. Thestate of stabilizer bar 144 is communicated by controller 102 to powersteering controller 246. In one embodiment, power steering controller246 applies more steering assist when stabilizer bar 144 is disengagedand/or at low stiffness levels than when stabilizer bar 144 is engagedand/or at high stiffness levels. In one embodiment, the level of powersteering assist may be inversely proportional (linearly or at multiplediscrete levels) to the level of stiffness of stabilizer bar 144.

Referring again to FIG. 5, in another embodiment controller 246implements a fixed assist mode at block 320 as the alternative powersteering control scheme of block 308. In this embodiment, when theground speed error is detected at block 304 of FIG. 5, controller 246applies a steering torque assist curve that corresponds to a preselectedfixed vehicle speed. For example, controller 246 applies steering torqueassist based on a stored torque assist curve for a particular groundspeed, such as 30 mph or any other suitable ground speed. Accordingly,the steering torque assist level varies according to the user torqueinput 240 and the assist curve corresponding to the selected fixedground speed. The steering torque assist level in the fixed assist modeof block 320 may vary further based on other inputs, such as thedriveline condition, transmission clutch engagement speed, and/orstabilizer bar configuration described herein.

Controller 246 of power steering unit 252 is further operative toexecute a self-diagnosis to determine whether a torque bias or offsethas drifted from a factory programmed offset (i.e., from a referencecalibration). The factory programmed offset may be initially zero or anyother suitable torque offset. The factory programmed offset isconfigured to zero or align the steering system when no external forcesare applied to the steering system, such as, for example, a usersteering torque input or a force applied to the wheel by an externalobject. In one embodiment, the torque offset is determined based on asensed position of a shaft of the steering unit 252 relative to areference position. For example, the offset may be determined via atorque or position sensor based on a rotational position of an inputshaft of power steering unit 252 relative to an output shaft of powersteering unit 252. In one embodiment, the torque offset is determinedbased on a detected change in the location of the torque sensor on thepower steering system, e.g., on a steering shaft. Controller 246 isoperative to perform an operation to automatically detect and correct adrifted torque offset, as described below.

The calibration of the power steering unit 252 may become inaccurate,for example, due to an impact to a shaft of the unit 252 or steeringassembly or due to other conditions. In some conditions, a driftedoffset bias of the power steering unit 252 may result in a left or rightsteering bias wherein the unit 252 improperly applies greater torqueassist in one turning direction than in another turning direction. As anexample, a 10 Newton meter (Nm) offset bias in power steering unit 252may cause up to a 10% bias to the controlled output torque assist level.

In the illustrated embodiment, controller 246 performs a self-check ateach ignition cycle of vehicle 10 and therefore at each power-up of unit252. Vehicle 10 is normally “at-rest” at power-up in that the steeringassembly normally has no external forces applied to it. For example, theuser input torque via steering wheel 182 (FIG. 3) and other externalsteering forces are zero in most at-rest conditions. Controller 246detects the input torque using torque sensing device 248 (FIG. 4), asdescribed herein. In one embodiment, the input torque is determined bythe angular displacement (i.e., offset) between two steering shafts ofsteering assembly 180 (FIG. 3), such as the input steering shaft 250 andoutput steering shaft 264 of FIG. 3. Other suitable methods ofdetermining input torque may be provided. The input torque is positivefor one steering direction and negative for the opposite steeringdirection.

If a detected input torque or angular difference is outside a tolerancerange stored in memory at vehicle power-up, the device records thedeviation in non-volatile memory, as described herein. The tolerancerange may include, for example, a lower limit of −2 Nm torque differenceand an upper limit of +2 Nm torque difference from the expected zerooffset in the at-rest condition, although any suitable tolerance rangemay be provided. After a predetermined number of ignition cycles wherethe detected input torque or angular displacement is out of range,controller 246 applies incremental or gradual correction factors atsubsequent power up events until the unit 252 reaches a point when themonitored angular difference is within the tolerance window or range atstartup. Controller 246 may log data at every startup or only onstartups when the parameter(s) are out of range. The self-check sequencemay be stored as code in memory accessible by controller 246.

FIG. 7 illustrates a flow diagram 350 of an exemplary method executed bycontroller 246 of FIG. 4 of self-checking the calibration of the powersteering unit 252. At block 352, power steering unit 252 powers upfollowing the ignition cycle, and controller 246 determines the angulardifference between the input and output steering shafts, i.e., the inputtorque to steering assembly 180. At block 356, controller 246 determineswhether the input/output angular difference is greater than an upperlimit preset tolerance value stored in memory. If the difference exceedsthe upper limit preset tolerance value at block 356, controller 246increments a Counter A by 1 and decrements a Counter B by 1 at block358. At block 360, if the Counter A is greater than or equal to a valueof 20, controller 246 executes the self-heal process at block 362, asdescribed herein with respect to FIG. 8. If the Counter A is less than20 at block 360, controller 246 determines that the self-heal process isnot yet required at block 376 and execution of method 350 is completeuntil the next ignition cycle.

If the input/output difference is not greater than the upper limitpreset tolerance value at block 356 but is less than the lower limitpreset tolerance value at block 364, controller 246 increments theCounter B by 1 and decrements the Counter A by 1 at block 366. In oneembodiment, the lower limit preset tolerance value is a negative numberindicative of an offset in the opposite steering direction. At block368, if the Counter B is greater than or equal to a value of 20,controller 246 executes the self-heal process at block 370, as describedherein with respect to FIG. 8. If the Counter B is less than 20 at block368, controller 246 determines that the self-heal process is notrequired at block 376 and execution of method 350 is complete until thenext ignition cycle.

As such, controller 246 initiates the self-heal process after athreshold consecutive number (e.g., 20=A=B) of ignition cycles where thecalibration offset of the power steering unit 252 is either greater thanthe upper tolerance value or less than the lower tolerance value. In oneembodiment, the requirement for a threshold number of consecutiveinstances when the calibration offset is out of the tolerance rangeserves to reduce the likelihood of initiating the self-heal processunder improper conditions. For example, if the detected input torque isdue to acceptable external forces such as an operator applying steeringtorque at startup or the wheel being parked at an angle against anobject at startup, the self-heal process should not be executed.

If the input/output angular difference is within the tolerance range,controller 246 determines at block 372 that the power steering unit 252is operating within the correct calibration tolerance. In oneembodiment, controller 246 increments a Counter C by 1 at block 372. Atblock 374, if Counter C is greater than 1000, Counter C is held at 1000.As such, controller 246 illustratively keeps a record of the number ofconsecutive ignition cycles (illustratively up to 1000 cycles) that thepower steering unit 252 is within the calibration tolerance range. Atblock 376, controller 246 determines that the self-heal process is notrequired and execution of method 350 is complete until the next ignitioncycle.

In some embodiments, controller 246 performs a consistency check for theout of tolerance condition to expedite execution of the self-healprocess. For example, at each execution of method 350 (illustratively ateach ignition cycle), controller 246 compares the last measured out oftolerance value (e.g., the previous input/output angular differencemeasured at the previous ignition cycle) to the currently measured outof tolerance value (e.g., the current input/output angular difference).If the last measured out of tolerance value is within a threshold rangeR of the currently measured out of tolerance value for a predeterminedconsecutive number of ignition cycles, the self-heal process isinitiated after the predetermined consecutive number of ignition cycles,which is less than the Counters A or B. For example, the predeterminedconsecutive number of ignition cycles may be five or ten or any suitablethreshold number less than Counters A and B. The threshold range R maybe any suitable range, such as within 1 or 2 nm. Accordingly, in thisembodiment, if a same or similar out of tolerance value is observed in athreshold number of consecutive ignition cycles, the self-heal processis initiated prior to reaching the number identified with Counters A orB to expedite the self-heal process.

When controller 246 determines that the self-heal process is required atblock 362 or block 370 of FIG. 7, controller 246 executes the self-healprocess. Referring to FIG. 8, an exemplary self-heal method for positiveor negative offset correction is illustrated in flow diagram 380 andbegins at block 382. At block 384, controller 246 calculates an amountof offset correction. In the illustrated embodiment, controller 246determines the offset correction by dividing the current detected offset(e.g., the input/output angular difference) by Counter A for positiveoffset or by Counter B for negative offset. Controller 246 multipliesthat product by Multiplier Z. Multiplier Z is a multiplier used toincrease or decrease the amount of incremental offset correction that isapplied per iteration of the self-heal process. For example, if A and Zfor positive offset (or B and Z for negative offset) are both equal to20, the amount of offset correction equals the amount of the detectedoffset, and the entire offset correction is applied at once. If Z isless than the value of the applicable Counter A or B, a fractionalamount of correction is applied. For example, if Z equals 1 and CounterA (or B) equals 20, then one twentieth of the detected current offset isapplied as the correction offset on this iteration. As such, anincremental adjustment to the calibration is calculated and implementedby controller 246. After a number of ignition cycles, the incrementalcorrections will eventually bring the offset to within the tolerancerange. Other suitable formulas for calculating the offset correctionamount may be provided.

If the detected offset is positive, the offset correction has a negativevalue, and if the detected offset is negative, the offset correction hasa positive value, thereby bringing the actual offset back withintolerance range. At block 386, controller 246 updates the offsetcalibration in memory based on the offset correction amount and appliesthe offset correction to power steering unit 252. In one embodiment,controller 246 applies the offset correction by compensating for theoffset correction in the power steering assist commands to motor 252(FIG. 3). At block 288, controller 246 optionally resets the countersincluding Counter A (for positive offset correction), Counter B (fornegative offset correction), and Counter C.

In some embodiments, for existing power steering units 252 that have anoffset bias with one or more components (e.g., steering shafts), fasterself-healing may be accomplished by continuously cycling the ignition onand off to simulate multiple days or weeks of operator usage in ashorter time (e.g., in minutes). For example, a dealer may cycle theignition multiple times over a short period so that controller 246applies the incremental changes to the offset at an accelerated rate.Controller 246 may also be programmed to implement the self-check ofFIG. 7 upon detecting a triggering event other than an ignition cycle,such as a user input requesting a self-check or a pre-ignitionbattery-on event, for example. In some embodiments, controller 246 isoperative to detect leaky bucket type counters, to reset the Counters Aand B to zero on predetermined events, and/or to implement acceleratedcounter conditions for use by a dealer to invoke a rapid heal condition.

Referring to FIG. 9, controller 102 of FIG. 2 is further operative toexecute a throttle override control for vehicle 10. FIG. 9 illustrates aflow diagram 400 of an exemplary method of overriding control ofthrottle valve 114 (FIG. 2) when brake operator 134 of FIG. 2 (or thevehicle brake) is applied. In some embodiments, the throttle overridemethod of FIG. 9 serves to release a stuck or jammed throttle valve 114or to close the throttle valve 114 when throttle operator 126 is stuckor jammed. In some embodiments, the brake throttle override method ofFIG. 9 serves to reduce the likelihood of the brake and the throttlebeing applied at the same time. Reference is made to FIG. 2 throughoutthe following description of FIG. 9.

At block 401, controller 102 detects application of the throttle. Forexample, controller 102 may detect a displacement of at least one ofthrottle operator 126 and throttle valve 114 to detect application ofthe throttle. At block 402, controller 102 detects the application ofbrake operator 134 (e.g., brake pedal) based on a signal output frombrake operator sensor 136. In the illustrated embodiment, brake operatorsensor 136 is operative to detect at least one of a pressure applied tobrake operator 134 and a displacement of brake operator 134. If theopening or position of throttle valve 114 (or the displacement ofthrottle operator 126) is greater than or equal to a first threshold atblock 404, and if the detected brake operator pressure (or brakeoperator displacement) is greater than or equal to a second threshold atblock 408, controller 102 reduces the opening of throttle valve 114 atblock 410 regardless of an operator demand for a greater throttle valveopening. In one embodiment, controller 102 closes the throttle valve 114at block 410 to a zero percent opening. In another embodiment,controller 102 reduces the opening of throttle valve 114 to at or belowthe first threshold opening.

In some embodiments, controller 102 waits a predetermined delay afterdetecting the brake application before reducing the throttle opening acalibrated amount. For example, upon detecting the brake operatorpressure or displacement exceeding the second threshold at block 408 fora threshold time (e.g., one second, two seconds, or any suitable delay),controller 102 then reduces the throttle opening at block 410. In someembodiments, reducing the throttle opening at block 410 includescalibrating a ramp down of the throttle opening. In particular, thethrottle valve opening is gradually reduced to the target reducedopening in response to the detected brake application exceeding thethreshold.

In some embodiments, the first threshold of block 404 may be a zeropercent throttle opening, a five percent throttle opening, or anothersuitable throttle opening. In some embodiments, the second threshold ofblock 408 may be a five percent total applied pressure or a five percentdisplacement of brake operator 134 or another suitable pressure ordisplacement value. In one embodiment, the first and second thresholdsare adjustable by the operator or dealer based on user input providedvia the user interface of vehicle 10. In an alternative embodiment, theposition of the vehicle brake may be detected at block 402 and comparedwith a corresponding threshold at block 408.

If the throttle valve opening at block 404 is less than the firstthreshold value, or if the brake pressure or displacement at block 408is less than the second threshold value, controller 102 does notintervene to close or reduce the opening of throttle valve 114, asrepresented at block 406.

Controller 102 of FIG. 2 is further operative to provide stabilitycontrol to vehicle 10. Referring to FIG. 10, an exemplary stabilitycontrol system 500 is illustrated. Controller 102 includes stabilitycontrol logic 502 operative to implement various control measures tostabilize vehicle 10 during vehicle operation based on monitored vehicleparameters. Controller 102 receives inputs 501 from sensors such as tirepressure, an operation selection mode (e.g., racing mode, sand dunemode, trail riding mode, work mode, snow/ice mode, etc.), load sensoroutput, accelerometer output, inclinometer output, steering angle,suspension and shock position, selected driveline mode (e.g., 2WD or4WD, state of differential, transmission gear, etc.), and other suitableinputs. In one embodiment, the controller 102 receives inputs fromthree-axis accelerometers and three-axis gyroscopes mounted to vehicle10. In one embodiment, an accelerometer and gyroscope are mounted insidean engine control unit (ECU) of vehicle 10 (e.g., controller 102). Basedon one or more of inputs 501, stability control logic 502 activelycontrols various systems and subsystems to improve the stability ofvehicle 10.

For example, stability control logic 502 adjusts the shocks and springsof the suspension system 504 of vehicle 10 to improve stability. Foradditional detail on damping control and adjustment of shock absorbersand springs, see U.S. application Ser. No. 14/074,340, filed Nov. 7,2013, and U.S. application Ser. No. 14/507,355, filed Oct. 6, 2014, bothentitled VEHICLE HAVING SUSPENSION WITH CONTINUOUS DAMPING CONTROL, theentire disclosures of which are expressly incorporated by referenceherein.

In one embodiment, stability control logic 502 controls the throttlevalve 114 and brakes 506 of vehicle 10 to provide stability control invarious vehicle conditions. In one embodiment, logic 502 locks andunlocks differentials 145 (FIG. 2) of driveline 508 to provideadditional vehicle stability. In one embodiment, logic 502 engages andadjusts the stiffness of torsion (stabilizer) bar 144 to provideadditional vehicle stability. In one embodiment, controller 102 furthercontrols one or more moveable masses 512 to adjust vehicle weightdistribution, as described herein.

FIG. 11 illustrates a flow diagram 550 of an exemplary method ofcontrolling vehicle stability based on various terrains traversed byvehicle 10. At block 551, controller 102 detects a drivelineconfiguration selected by an operator based on user input and sensoroutput. As described herein, the driveline configuration includes thenumber of driven wheels (e.g., 2WD or 4WD), the state of thedifferential (e.g., open, locked, or controlled slip), and/or theselected transmission gear ratio. At block 551, controller 102 alsodetects an operation selection mode (e.g., racing mode, sand dune mode,trail riding mode, work mode, snow/ice mode, etc.) selected by a uservia mode selector 118 (FIG. 2), as described herein. At block 552,controller 102 detects a wheel speed of vehicle 10 based on output fromspeed sensor 110 (FIG. 2). At block 554, controller 102 determines oneor more vehicle accelerations. For example, controller 102 determinesthe wheel acceleration based on the detected wheel speed and linear andangular accelerations of vehicle 10 based on accelerometer output. Atblock 556, controller 102 monitors the suspension displacement based onoutput from one or more suspension sensors 138 (FIG. 2). For example, ashock position at each wheel may be monitored at block 556 to detect acompression or expansion of the shocks or springs, and a suspensionposition may be monitored at block 556 to detect the height of thechassis relative to the wheels. At block 557, controller 102 monitorsthe steering angle of the steering assembly, such as steering assembly180 of FIG. 3.

At block 558, controller 102 compares the detected parameters, includingfor example the wheel speed, wheel and vehicle accelerations, thesuspension displacement, and the steering angle, to correspondingthresholds defined in a parameter map 510 calibrated for variousterrains traversed by the vehicle 10. Parameter map 510 isillustratively stored in memory of controller 102 (FIG. 10). The definedparameter map 510 provides thresholds for various terrain conditions. Inone embodiment, one or more thresholds in defined parameter map 510 arebased on the driveline configuration of vehicle 10 and an operationselection mode identified at block 551 (e.g., racing mode, sand dunemode, trail riding mode, work mode, snow/ice mode, etc.). For example,one or more thresholds in defined parameter map 510 have differentvalues for different driveline conditions and operation modes. Based onthe comparison of the detected parameters to the thresholds in definedparameter map 510, controller 102 is operative to adjust active systemsof vehicle 10 at block 560 to improve vehicle stability in differentterrain conditions.

For example, suspension displacement is monitored and compared to thedetected vehicle speed to determine the rate the shocks are moving atthe detected vehicle speed. As the suspension displacement rate exceedsvarious thresholds at different speeds, the harshness or smoothness ofthe terrain may be determined and adjustment to active systems may beimplemented. A comparison of accelerometer output to accelerationthresholds is also used to determine the harshness of the terrain, suchas to determine the suspension displacement rate and/or to detect suddenaccelerations (e.g., angular or linear) of vehicle 10 in variousdirections due to bumpy terrain. Further, wheel acceleration incombination with shock displacement and accelerometer output is used bycontroller 102 to determine slick or low traction conditions, such aswith ice/snow, gravel, or sand terrains. Based on the wheel speed, theshock displacement, the rate of shock displacement, vehicleaccelerations, and/or driveline configuration, controller 102 determinesthe harshness or roughness of the terrain based on the defined parametermap 510.

Controller 102 at block 560 adjusts the operation and calibration of oneor more active systems of vehicle 10 to provide improved stability forvehicle 10 based on the comparisons of block 558. For example, one ormore active systems are adjusted by controller 102 in response to aharsher or smoother terrain. In one embodiment, the active systems areadjusted based on the defined parameter map 510 according to thedriveline configuration and the operation selection mode, as describedherein. Exemplary active systems that are adjusted at block 560 includesuspension (e.g., shock and/or spring damping and vehicle height),stabilizer bar 144, braking, electronic throttle control, powersteering, moveable masses 512, transmission gear, and drivelineconfiguration (4WD vs 2WD, differential engagement, etc.). Controller102 actively monitors feedback from each of these systems and adjuststhe configuration of one or more of these systems to dynamically improvevehicle stability.

In one embodiment, controller 102 uses parameter map 510 to adjust thestiffness of the suspension system 139 (FIG. 2), including the shocksand/or springs, based on the terrain. For example, low suspensiondisplacement at higher vehicle speeds is indicative of a smooth terrain,such as a road terrain, for example. Accordingly, upon detection of thesuspension displacement and/or displacement rate being below a firstdisplacement threshold and the vehicle speed exceeding a high speedthreshold, controller 102 increases the stiffness of suspension system139. Upon detection of the suspension displacement and/or displacementrate exceeding a second displacement threshold and the vehicle speedbeing below a low speed threshold, which is indicative of a roughterrain, controller 102 decreases the stiffness of suspension system 139to soften vehicle 10. In one embodiment, the first displacementthreshold is less than the second displacement threshold. In oneembodiment, the low speed threshold is less than the high speedthreshold, although the low and high speed thresholds may alternativelybe the same. The stiffness of the suspension may be adjusted based on afluid level in the shocks or a position of the shocks or springs, asdescribed in U.S. application Ser. No. 14/507,355, filed Oct. 6, 2014,entitled VEHICLE HAVING SUSPENSION WITH CONTINUOUS DAMPING CONTROL.

In one embodiment, controller 102 uses parameter map 510 to adjust thevehicle ride height (load level) of vehicle 10 based on the terrain. Thevehicle ride height is adjusted with suspension system 139, such as byadjusting the position of the springs or shocks. In one embodiment,controller 102 lowers the vehicle ride height in response to detectingrough terrain, i.e., detecting the suspension displacement and/ordisplacement rate exceeding a threshold for a corresponding vehiclespeed. Further, controller 102 lowers the vehicle ride height in smoothterrain at high vehicle speeds. For example, in response to thesuspension displacement and/or displacement rate being below a thresholdand the vehicle speed exceeding a high speed threshold, controller 102lowers the vehicle ride height by a predetermined amount.

In one embodiment, controller 102 uses parameter map 510 to adjust thestiffness of stabilizer bar 144 (FIG. 2) based on the terrain. Inresponse to detecting smooth terrain, controller 102 increases thestiffness of stabilizer bar 144. In response to detecting rough terrain,controller 102 decreases the stiffness of stabilizer bar 144. The smoothand rough terrain is detected based on displacement and speed thresholdsof parameter map 510 as described above.

In one embodiment, controller 102 uses parameter map 510 to adjust thedriveline configuration based on the terrain. For example, controller102 changes the driveline between 2WD and 4WD configurations and/orbetween states of the differential based on the terrain. The smooth andrough terrain is detected based on displacement and speed thresholds ofparameter map 510 as described above. In one embodiment, controller 102changes the driveline configuration by changing from an open or lockedstate of the differential to a controlled slip state. In the controlledslip state, the controller adjusts a slip of the differential based on adetected steering angle and a detected yaw rate of the vehicle.

In one embodiment, controller 102 is further operative to activelycontrol one or more active systems upon detection of an airbornecondition to improve the trajectory and landing of vehicle 10. See, forexample, the exemplary airborne controls disclosed in U.S. patentapplication Ser. No. 13/652,253, filed Oct. 15, 2012, entitled PRIMARYCLUTCH ELECTRONIC CVT, the entire disclosure of which is expresslyincorporated by reference herein.

In some embodiments, components and systems of vehicle 10 are packagedfor improved weight distribution depending on the intended vehicle use.Vehicle 10 may be manufactured with a different weight distributiondepending on the vehicle model. For example, the manufacturer mayreceive an order that identifies a targeted operating environment of thevehicle, such as trail riding, work operations, racing, etc. Themanufacturer configures the weight distribution of the vehicle based onthe intended operating environment. For example, for a vehicle 10 thatis intended for racing or airborne conditions, the vehicle 10 may beconfigured such that a greater mass is towards the front and rear endsof the vehicle 10 to provide additional stability in the air. Componentssuch as engine 130, the radiator, generator, engine crank shaft, sparetire, fake weight, and/or battery 109 (FIG. 2) are therefore positionedcloser to the front or rear ends of vehicle 10 for improved weightdistribution and improved pitch inertia. Similarly, for a vehicle 10intended for slower speeds and tight turns and not intended for airborneconditions, such as for trail riding or work operations, the mass ispositioned more towards the center of the vehicle 10 to provide lesspitch inertia.

In some embodiments, vehicle 10 includes one or more movable masses 512(FIG. 10) to allow an operator or dealer to vary the weight distributionof vehicle 10 after purchase of the vehicle 10. The moveable masses 512are either automatically moved by actuators of vehicle 10 controlled bycontroller 102 or manually moved by an operator prior to vehicleoperation. For example, vehicle 10 may be configured such that anoperator or dealer manually moves the location of various components onthe vehicle 10, such as the battery 109, radiator, seat, generator,engine crank shaft, spare tire, fake weight, or other suitablecomponents, based on the intended operating environment. In anotherembodiment, the operator selects an operation selection mode via modeselector 118 (FIG. 2), and controller 102 automatically controlsactuators to move the moveable masses 512 based on the selectedoperation mode. For example, controller 102 moves masses 512 towards thefront and rear ends of vehicle 10 in response to user selection of asand dune mode or racing mode, and controller 102 moves masses 512towards the center of vehicle 10 in response to user selection of atrail mode or work mode. Further, vehicle 10 may include a spare tirecarrier that is attached to the rear end of vehicle 10 for improvedweight distribution. The spare tire carrier may be filled with water toadd additional mass. Further still, a detachable front or rear bumpermay be provided to add mass to an end of vehicle 10. In addition,flywheels may be mounted to vehicle 10 to further target a specificweight distribution of vehicle 10.

In some embodiments, stability control system 500 of FIG. 10 isoperative to automatically vary the location of one or more movablemasses 512 (FIG. 10) actively during vehicle operation. For example,moveable masses 512 include a flywheel system or gyroscope systemcontrolled by controller 102 to actively adjust mass distribution duringvehicle operation based on the detected vehicle stability and/ordetected terrain. The vehicle stability is detected by controller 102based on various inputs such as vehicle speed, acceleration, operationmode, vehicle pitch or tilt, and other inputs. For example, a flywheelor gyroscope system is shifted during an airborne condition of vehicle10 to level the vehicle 10 in response to detection of a vehicle pitchthat exceeds a threshold, i.e., a vehicle pitch indicative of a nosedive or non-level condition. The flywheel or gyroscope system is alsoused to shift mass during turning or cornering operations of vehicle 10.In another embodiment, controller 102 automatically controls theapplication of the throttle and/or brake during the airborne conditionto further improve the pitch of vehicle 10. For example, controller 102selectively increases the throttle opening to increase driveline inertiaand thereby cause the front end of the vehicle 10 to pitch up relativeto the rear end of the vehicle, and controller 102 selectively appliesthe brakes to cause the front end of vehicle 10 to pitch downwardrelative to the rear end of vehicle 10.

In some embodiments, vehicle stability is improved by decreasing asteering speed of the steering rack (steering ratio). In someembodiments, the steering rack 258 of FIG. 3 is controlled to have avariable ratio based on vehicle speed. For example, for faster vehiclespeeds the steering rack 258 has a lower speed and for slower vehiclespeeds the rack 258 has a faster speed. In some embodiments, thesteering rack ratio is controlled based on operation selection modesprogrammed into controller 102 of FIG. 2. For example, each drive modehas a variable speed ratio of the steering rack 258 to provide varyingsteering response based on desired vehicle performance.

In some embodiments, vehicle stability is improved by biasing the speedsof each driven wheel (e.g., wheels 24 a, 24 b of FIG. 1) for varioussteering conditions. Oversteering of vehicle 10 may occur when vehicle10 has a low steering angle and a high yaw rate, and understeering ofvehicle 10 may occur when vehicle 10 has a high steering angle and a lowyaw rate. In some embodiments, controller 102 is operative to vary therelative speeds of individual wheels to reduce the oversteering orundersteering of vehicle 10. For example, controller 102 adjusts thespeeds of each wheel 24 a, 24 b to achieve target wheel speeds forcertain steering angles of vehicle 10. In one embodiment, a motor iscoupled to each differential (e.g., front, rear, and/or centerdifferential) to control speed variations of each wheel 24 a, 24 b.Alternatively, a motor is coupled to each driven wheel to vary the speedof the corresponding wheel relative to other driven wheels. Controller102 controls the motor(s) to vary individual wheel speeds based on thesteering angle, the vehicle speed, and yaw or acceleration rates ofvehicle 10. In one embodiment, braking of one or more wheels is furtherused to reduce oversteering and understeering of vehicle.

While this invention has been described as having an exemplary design,the present invention may be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains.

What is claimed is:
 1. A power steering method for a vehicle, the methodincluding: detecting, by a controller of a power steering system, aselected gear of a transmission of the vehicle; determining, by thecontroller, a power steering assist level based on the selected gear ofthe transmission and a user torque input to a steering assembly of thevehicle; and outputting, by the power steering system, steering torqueassistance to the steering assembly of the vehicle based on the powersteering assist level.
 2. The method of claim 1, wherein the controllerdetermines a first power steering assist level for a low range gear ofthe transmission and a second power steering assist level for a highrange gear of the transmission, the first power steering assist levelbeing greater than the second power steering assist level.
 3. The methodof claim 1, further including detecting a ground speed of the vehiclebased on output from a ground speed sensor, wherein the determining thepower steering assist level is further based on the detected groundspeed.
 4. The method of claim 3, wherein the power steering assist levelfor a same selected gear of the transmission is greater for low groundspeeds than for high ground speeds.
 5. The method of claim 1, furtherincluding estimating, by the controller, a ground speed of the vehiclebased on the engine speed, a predetermined maximum engine speed, and apredetermined maximum ground speed, wherein the determining the powersteering assist level is further based on the estimated ground speed. 6.The method of claim 1, further including detecting a driveline conditionof the vehicle, the determining the power steering assist level furtherbeing based on the driveline condition, wherein the driveline conditionincludes at least one of a number of wheels driven by the engine and astate of a differential of the driveline.
 7. The method of claim 1,further including detecting a state of a stabilizer bar coupled to thesteering assembly of the vehicle, the determining the power steeringassist level further being based on the state of the stabilizer bar, thestate of the stabilizer bar including at least one of an engaged state,a disengaged state, and a stiffness level of the stabilizer bar.